The invention relates to a process for preparing N,N-substituted carbamoyl halides. In one aspect, the invention relates to a new and useful process for preparing N,N-substituted carbamoyl halides from secondary amines, carbon dioxide and a halide-containing electrophilic compound.
Carbamoyl halides, particularly carbamoyl chlorides, are useful intermediates in the preparation of unsymmetrical ureas and N,N-dialkyl carbamate esters. Carbamoyl chlorides are useful intermediates in the preparation of amides in direct Friedel-Crafts acylation of aromatics and the resulting amides can be hydrolyzed to the corresponding carboxylic acids. Carbamoyl chlorides are also useful intermediates in the preparation of thiocarbamate herbicides via the reaction of carbamoyl chlorides with a thiol (as the sodium alkylmercaptide).
Commercially, the phosgenation of ammonia and amines is by far the most widely used method for producing carbamoyl chlorides. For the preparation of N,N-substituted carbamoyl chlorides, the commercial process involves the phosgenation of secondary amine. The use of phosgene, however, has several disadvantages. The phosgenation route is long, energy intensive and requires handling highly corrosive materials, e.g. hydrogen chloride and chlorine, and highly toxic reagents and intermediates, e.g. phosgene and chlorine. Furthermore, the phosgenation route requires use of process equipment which can withstand high temperatures and highly corrosive conditions resulting in increased capital cost.
A non-phosgene process for preparing N,N-substituted carbamoyl halides which is economical, commercially viable and can produce N,N-substituted carbamoyl halides with good yields under extremely mild reaction conditions and short reaction times is highly desirable.